Interface device for converting a computer printer port into an input/output port

BACKGROUND OF THE INVENTION

The present invention relates to a novel interface device, which permits a universal input/output to personal computers (hereinafter simply referred to as "PCs"), by using a printer port which is found on most PCs.

In general, the printer port of the PC is composed of DATA lines for sending out characters or graphic data to be printed by a printer, a STB line for sending out a synchronizing output signal allowing data to be read in the printer, that is, a STB (STROBE) (hereinafter abbreviated) signal, a READY line for receiving a signal informing whether or not data can be read in from the printer, that is, a READY (or BUSY) signal, and an ACK line for receiving a data required pulse from the printer, that is, an ACK (ACKNOWLEDGE) (hereinafter abbreviated) signal (hereinafter the upper bar " " is omitted).

The timing chart of the DATA signal at the printer port in the PC and the control signals which are composed of STB, READY and ACK signals is as shown in FIG. 1. In the PC, first of all, a datum which is necessary for the DATA line is sent out, and then, a STB pulse requiring data to be read is developed as an output. The printer which has received the STB pulse makes the level of the READY signal high (H) so as to read the data (shown by the dotted lines (a) and (a') in FIG. 1). When the operations, for example, of reading the data or printing comes to an end, the level of the READY signal is made low (L) so as to supply the pulse (ACK), which requires data, as an input to the PC. Otherwise, the pulse (ACK) is supplied as an input to the PC as shown by the dotted line, so that the level of the READY signal is made low (L) in response to the rise thereof. The PC which has received the same prepares the next DATA (shown by the dotted line (b) in FIG. 1), and the STB signal is again developed as an output.

The sending and receiving of signals as stated above is relatively well standardized, and similar signal lines are used in PCs of different manufacturers. Therefore, the interface means, to which are connected machines and instruments via the printer port, is generally applicable to all such PCs.

However, since the main object of the printer port is that of transferring the printing data, the input to the PC is limited to the READY and ACK signals and the like even if the data are parallel data, and the role thereof is so determined. Therefore, if the printer port is used as an input/output port, the input information line to the PC would not be sufficient.

SUMMARY OF THE INVENTION

The present invention is an interface device in which the printer port of a PC can be used as an input/output port of other than the printer. The present invention provides an interface means which is adapted to increase the information input to the PC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a timing chart of the input/output signals at the printer port of a PC; and

FIGS. 2 and 3 are block diagrams respectively showing embodiments of the interface means in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the present invention will be described with reference to FIGS. 2 and 3.

FIG. 2 shows one embodiment in accordance with the present invention. In FIG. 2, 1₁ -1_n are DATA terminals, 2 is a STB terminal, 3 is a READY terminal and 4 is an ACK terminal. These are respectively connected to the lines to which they correspond in the printer port in the PC, so that signals are sent and received by the PC. The DATA teminals 1₁ -1_n are connected to the inputs of data latch circuits 6₁ -6_n, the data latch trigger terminals 5₁ -5_n of which are connected to the STB terminal 2. The outputs of the data latch circuits 6₁ -6_n are connected respectively to one input of NAND circuits 8₁ -8_n, the other inputs of which are connected to sensors 7₁ -7_n. The outputs of the NAND circuits 8₁ -8_n are connected to the READY terminal 3, and also to the input of a one-shot multivibrator 9, the output of which is connected to the ACK terminal 4.

Each of the above-mentioned NAND circuits 8₁ -8_n is provided with an output terminal of an open collector type, and the outputs are connected in parallel so as to form a wired OR connection.

Data at the DATA terminals 1₁ -1_n are latched in the data latch circuits 6₁ -6_n by the signals at the STB terminal 2. Now, if the datum of the terminal 1₁ is at the H level and the data at the other terminals 1₂ -1_n are at the L level, the outputs of the NAND circuits 8₂ -8_n are at the H level without regard to whether the outputs of the sensors 7₂ -7_n are at the H level or the L level. On the other hand, the output of the NAND circuit 8₁ varies so as to be at the L level when the output of the sensor 7₁ is at the H level and be at the H level when the output of the sensor 7₁ is at the L level. In other words, the PC is able to detect the state of the sensor 7₁ by setting the DATA terminal 1₁ at the H level and the other DATA terminals 1₂ - 1_n at the L level. If the DATA terminal 1₂ is set at the H level and the other DATA terminals are set at the L level, it is possible to determine the state of the sensor 7₂. Likewise, if the DATA terminal 1_n is set at the H level and the other DATA terminals are set at the L level, it is possible to determine the state of the sensor 7_n.

FIG. 3 shows an example applied to the control of a mechanical device, that is, a winch 13 for driving a load 11 by means of a motor 12, by the PC. The motor control circuit 14 is adapted to operate such that the winch 13 is rotated counterclockwise to raise load 11 when the datum from the DATA terminal 1₁ which is latched by the data latch circuit 6 is at the H level and the datum from the terminal 1₂ is at the L level. On the other hand, the READY terminal 3 is kept at the H level unitl one of the inputs of the NAND circuit 8₁ is at the H level and the upper limit switch (sensor) 7₁ is turned on. If the upper limit is reached so that the switch 7₁ is turned on, the READY terminal is at the L level. At the same time, the ACK pulse is sent out to the ACK terminal 4 by the one-shot multivibrator 9. Conversely, when the load 11 is lowered, the PC may send out data such that the terminal 1₁ is at the L level and the terminal 1₂ is at the H level.

Although the data lines and the sensors are in one to one correspondence in accordance with the embodiments shown in FIGS. 2 and 3, it is also possible to permit selection of more sensors with fewer bit numbers if the data are subjected to logical operations by a logic circuit. For example, in the case of a datum of 8 bits, it is possible to make 256 selections.

Although the command to the interface means is also used for the selection of sensors in the embodiment shown in FIG. 3, it is also possible for the use of the data lines to be divided into two, that is, one for the command and the other for the selection of the sensors.

In accordance with the present invention as described hereinabove, since one sensor may be selected from among one or more sensors based on the data sent by way of the printer port of the PC, so that a signal based on the output is fed back to the printer port, it becomes possible to increase the feedback information for the command from the PC, thereby making it possible to perform more delicate control even if a printer port with fewer input terminals to the PC is used.